As for the method of producing water-soluble cationic polymer dispersions, which are used as auxiliary agents in papermaking or as flocculants in waste water treatment, by carrying out copolymerization using a cationic monomer prepared by quaternizing dimethylaminoethyl(meth)acrylate or the like with benzyl chloride or a hydrophobic alkyl monohalide, a method of producing polymers in a dispersed state is disclosed in Japanese Kokai Publication (Laid-open Japanese Patent Application; JP Kokai) S61-123610 and Japanese Kokai Publication H05-32722 which method comprises carrying out the polymerization in an aqueous salt solution, in which the monomer or copolymer comprising the above-mentioned cationic monomer is not soluble, in the presence of a polymer soluble in that aqueous salt solution.
This method has a drawback in that such a specific hydrophobic cationic monomer as the product of quaternization of dimethylaminoethyl(meth)acrylate or the like with benzyl chloride or a hydrophobic alkyl monohalide must be used as the cationic monomer. A homopolymer of dimethylaminoethyl(meth)acrylate or the like or a copolymer thereof with acrylamide or the like is used as the coexisting polymer soluble in an aqueous salt solution.
On the other hand, a method of producing dispersions comprising fine water-soluble polymer particles and, as a dispersion medium, an aqueous solution of a polymer such as polyethylene glycol is disclosed in Japanese S62-5170. Polyethylene glycol is not only expensive but also ineffective as an auxiliary agent in papermaking or as a flocculent. It is used in a large amount in the step of polymerization, thus causing an increase in raw material cost.
On the other hand, polyethylenimine, one of polyalkylenimines, is in use as a freeness improving agent or a yield aid in papermaking and, therefore, a water-soluble polymer dispersion in which a polyalkylenimine coexists is thought to have a very efficient form.
As mentioned above, water-soluble polymers are widely used in the paper industry as freeness improving agents and yield aids in the process of papermaking or agents for recovering valuable resources from white water, for instance. Further, they can be used also as oil separating agents to be used in the process of oil manufacturing or of oil separation and treatment of oil-containing industrial waste water, or as agents to be added to city sewage, human waste, general industrial waste water-derived raw sludge, biologically treated sludge, digested sludge, or mixed sludge derived therefrom, in the treatment thereof for flocculation or in dewatering in dewatering equipment following flocculation.
Thus, it is an object of the present invention to develop such water-soluble polymers that are industrially useful in the form of dispersions excellent in storage stability, fluidity and solubility and capable of being produced with ease using low cost production equipment, and to provide a producing method of the dispersions.